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MDEV-298: SHOW EXPLAIN: Plan returned by SHOW EXPLAIN only contains 'Using temporary' ...

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- Correct the way SHOW EXPLAIN code calculates 'need_order' parameter 
  for JOIN::print_explain(). 
  The calculation is still an approximation (see MDEV entry for details) (even EXPLAIN itself
  is wrong in certain cases), but now it's a better approximation than before.
This commit is contained in:
Sergey Petrunya 2012-07-20 01:52:03 +04:00
parent ab70b76d9c
commit 8950ed8fdd
3 changed files with 68 additions and 1 deletions
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38
mysql-test/r/show_explain.result
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@ -888,4 +888,42 @@ a+SLEEP(0.01)
0 0
set debug_dbug=''; set debug_dbug='';
drop table t1; drop table t1;
#
# MDEV-298: SHOW EXPLAIN: Plan returned by SHOW EXPLAIN only contains
# 'Using temporary' while the standard EXPLAIN says 'Using temporary; Using filesort'
#
CREATE TABLE t1 (a INT);
INSERT INTO t1 VALUES (1),(2),(3),(4),(5),(6),(7),(8),(9),
(10),(11),(12),(13),(14),(15),(16);
INSERT INTO t1 SELECT t11.a FROM t1 t11, t1 t12, t1 t13;
EXPLAIN SELECT a FROM t1 GROUP BY a;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ALL NULL NULL NULL NULL 4112 Using temporary; Using filesort
set @show_explain_probe_select_id=1;
set debug_dbug='d,show_explain_probe_join_exec_start';
SELECT a FROM t1 GROUP BY a;
show explain for $thr2;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ALL NULL NULL NULL NULL 4112 Using temporary; Using filesort
Warnings:
Note 1003 SELECT a FROM t1 GROUP BY a
a
1
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set debug_dbug='';
drop table t1;
drop table t0; drop table t0;

28
mysql-test/t/show_explain.test
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@ -919,5 +919,33 @@ reap;
set debug_dbug=''; set debug_dbug='';
drop table t1; drop table t1;
--echo #
--echo # MDEV-298: SHOW EXPLAIN: Plan returned by SHOW EXPLAIN only contains
--echo # 'Using temporary' while the standard EXPLAIN says 'Using temporary; Using filesort'
--echo #
CREATE TABLE t1 (a INT);
INSERT INTO t1 VALUES (1),(2),(3),(4),(5),(6),(7),(8),(9),
(10),(11),(12),(13),(14),(15),(16);
INSERT INTO t1 SELECT t11.a FROM t1 t11, t1 t12, t1 t13;
EXPLAIN SELECT a FROM t1 GROUP BY a;
set @show_explain_probe_select_id=1;
set debug_dbug='d,show_explain_probe_join_exec_start';
--send
SELECT a FROM t1 GROUP BY a;
connection default;
--source include/wait_condition.inc
evalp show explain for $thr2;
connection con1;
reap;
set debug_dbug='';
drop table t1;
drop table t0; drop table t0;

3
sql/sql_lex.cc
View File

@ -4100,7 +4100,8 @@ int st_select_lex::print_explain(select_result_sink *output,
{ {
res= join->print_explain(output, explain_flags, TRUE, res= join->print_explain(output, explain_flags, TRUE,
join->need_tmp, // need_tmp_table join->need_tmp, // need_tmp_table
(join->order != 0 && !join->skip_sort_order), // bool need_order !join->skip_sort_order && !join->no_order &&
(join->order || join->group_list), // bool need_order
join->select_distinct, // bool distinct join->select_distinct, // bool distinct
NULL); //const char *message NULL); //const char *message
} }